dft_tools/test/triqs/clef_examples/sum_functional.cpp

#include <triqs/clef.hpp>

template<typename Domain> struct sum_impl { 
 Domain d;

 // C++14 
 // double operator() (NotClefExpression const & f) const { double s=0; for (int u=0; u<10; ++u) s += f(u/10.0); return s;}

 // C++11 form 
 template <typename F>
  typename std::enable_if< !triqs::clef::is_clef_expression <F>::value, double >::type 
  operator() (F const & f) const { double s=0; for (int u=0; u<10; ++u) s += f(u/10.0); return s;}

 TRIQS_CLEF_IMPLEMENT_LAZY_CALL(sum_impl);

 friend std::ostream & operator<<(std::ostream & out, sum_impl const & x) { return out<<"sum";}
};

// a little factory ...
template<typename Domain> sum_impl<Domain> sum_functional (Domain d) {return {d};}

struct DOM{};

int main() { 
 triqs::clef::placeholder <1> x_; triqs::clef::placeholder <2> y_; 
 DOM d; 

 // integrate_on_d is the integration functional 
 auto integrate_on_d = sum_functional(d); 

 // This is a simple application of the sum to a function 
 std::cout<< integrate_on_d( x_ >> 2*x_ + 1 )  << std::endl;

 // A function y -> y_ + integrate (x -> 2*x + y) 
 auto e1 = y_ + integrate_on_d( x_ >> 2*x_  + y_ );
 std::cout<< e1 << std::endl;
 std::cout<< eval (e1 ,y_ =0)  << std::endl;
}